The use of ultraviolet (UV) light for the purpose of sterilizing a liquid is well known. A problem that arises with a turbid liquid is that the light does not penetrate very far into the liquid and hence liquid furthest from the UV lamp may not be sterilized at all or may not be properly sterilized.
South African patent specification 96/8029 discloses an elongate sterilizer in which a fluorescent tube is within, and co-axial with, an elongate housing. The sterilization chamber is between the fluorescent tube and the housing. The liquid inlet and liquid outlet are arranged tangentially with respect to the housing in an effort to cause the liquid to swirl and overcome the difficulty referred to above. It has been found, however, that the swirling motion imparted to the liquid as it enters the housing does not continue throughout the length of the housing, thus limiting the beneficial effect.
Other structures are known, such as that shown in U.S. Pat. No. 5,675,153, in which there is a helical vane in the space between the fluorescent tube and the housing, the vane extending from one end of the housing to the other. The vane is slotted and there is a gap between the vane and the inner surface of the housing. Such a structure would be completely unsuitable for the sterilization of milk, because of the many sharp corners where flow would stagnate and bacteria would be able to multiply.
There is a tendency for solids in milk to deposit on the surfaces defining the flow passage, in regions where there is insufficient flow velocity, so that the structure of U.S. Pat. No. 5,675,153 if it were to be used for the sterilization of milk, would suffer from deposits and as a consequence would require frequent cleaning. The structure would, in any event, be difficult to clean to the degree that is required in apparatus that is used for the handling of milk.